STCE Newsletter · STCE Newsletter 28 Dec 2015 - 3 Jan 2016 Page 7 of 18 2. PROBA2 Observations (28...

STCE Newsletter 28 Dec 2015 - 3 Jan 2016 Page 1 of 18

STCE Newsletter

28 Dec 2015 - 3 Jan 2016

Published by the STCE - this issue : 8 Jan 2016. Available onlineat http://www.stce.be/newsletter/ .

The Solar-Terrestrial Centre of Excellence (STCE) is acollaborative network of the Belgian Institute for SpaceAeronomy, the Royal Observatory of Belgium and the RoyalMeteorological Institute of Belgium.

Content Page

1. M-class brothers 2

2. PROBA2 Observations (28 Dec 2015 - 3 Jan 2016) 7

3. Review of solar activity 10

4. The International Sunspot Number (28 Dec 2015 - 3 Jan 2016 14

5. Noticeable Solar Events (28 Dec 2015 - 3 Jan 2016) 14

6. Review of geomagnetic activity 15

7. Geomagnetic Observations at Dourbes (28 Dec 2015 - 3 Jan 2016) 16

8. Review of ionospheric activity (28 Dec 2015 - 3 Jan 2016) 17

9. Future Events 18

Final Editor : Petra VanlommelContact : R. Van der Linden, General Coordinator STCE,

Ringlaan - 3 - Avenue Circulaire, 1180 Brussels,Belgium


1. M-class brothers

The two strongest events that occurred during last week were two M-class flares. They were both bornfrom active region (AR) NOAA 2473, which was also responsible for most of the M-class flaring the weekbefore. This region was declining in sunspot area, but remained magnetically complex throughout itsentire transit over the solar disk. So how do these two medium flares compare to each other?

Aside having the same sunspot group as their "mother", the two events shared some other similarities.They were both of about equal strength, the M1.8 flare peaking on 28 December at 12:45UT and theM2.3 flare peaking on 02 January at 00:11UT. The difference in timing (noon vs. midnight) implies thatany direct effect on communication or radar took place over nearly opposite parts of the Earth. Bothflares were also long duration events, lasting respectively 169 and 111 minutes. Note that the end time isthe time when the x-ray flux level decays to a point halfway between the maximum flux and the pre-flarebackground level. Hence, when there are no other actively flaring regions, one can follow the declineof the x-ray flux over a much longer timeframe than the timing of the flare's ending would suggest (seechart above). Another similarity was that the flares took place in about the same location of the AR, i.e. inthe mid to trailing section. Both were also parallel ribbon flares, as can be seen in the extreme ultraviolet(EUV) images underneath taken by SDO (AIA 1600 filter - see http://sdo.gsfc.nasa.gov/ ).


The main differences between the flares arose mainly from the different location on the solar disk whenthe flares were produced, as can be readily seen in the SDO/AIA131 images taken at the timing ofthe maximum x-ray flux. The M1 flare took place near disk centre slightly west of the central meridian(S19W09, i.e. 19 degrees south of the solar equator, 9 degrees west of the central meridian), whereasthe M2 flare occurred much closer to the west limb (S21W69).

The different location influenced the observed increase in proton flux significantly. Because of its muchmore western position, the M2 flare was magnetically a lot better connected to Earth than the M1 flare. As


a result (see graph underneath), the proton flux of the latter increased only very slowly, and reached itsmaximum only 9 hours after the x-ray peak, remaining well below the proton event threshold. Followingthe M2 flare, the proton flux increased very quickly and reached its maximum of 21 pfu (proton flux unit- see http://www.stce.be/news/325/welcome.html for more info) already on 02 January at 04:50UT. Agenuine, albeit minor, proton event!

Both flares were accompanied by impressive and complex series of post-flare coronal loops (a so-called"arcade"). Figure underneath provides a snapshot of the loops respectively 5 and 2 hours after themaximum x-ray flux was reached. The images are false colored SDO/AIA 171, to bring out the subtledetails of these delicate arches.


The aftermath of the flares was also characterized by different features. For example, during the decliningphase of the M1 flare there were a number of impressive jets visible emanating from the main leadingsunspot (see http://www.stce.be/news/293/welcome.html for more on jets). This can be seen in themovie at https://youtu.be/g1wLejwLKX4 in the false colored SDO/AIA 171 clip. On the other hand, theposition of the M2 flare offered a good view on the supra-arcade downflows. These are the dark streaks("tadpoles") that can be seen moving sunward to the top of the developing post-flare loops. The moviecontains a clip combining SDO/AIA 171 (yellow; moderate temperatures; loops) with SDO/AIA 131(bluish; high temperatures; downflows) imagery. See also the annotated image underneath. The origin ofthese downflows is not well understood yet. One of the theories supports the idea that these are plasmavoids following in the wake of shrinking magnetic flux tubes.


Finally, the difference in location of the flares obviously had its effect on the direction of the associatedcoronal mass ejection (CME). As can be seen in these coronagraphic images (CACTus - see http://www.sidc.oma.be/cactus/ ), the CME associated with the M1 flare was a partial halo CME, indicatingthat it had an Earth directed component. The CME associated with the M2 flare was much more solidand faster, but also not as wide and its bulk clearly directed away from the Sun-Earth line. In the end, thefirst CME caused a moderate geomagnetic storm a few days later, whereas the second CME apparentlymissed Earth and certainly did not leave an obvious signature in the solar wind parameters.


2. PROBA2 Observations (28 Dec 2015 - 3 Jan 2016)

Solar ActivitySolar flare activity fluctuated between very low and moderate during the week.In order to view the activity of this week in more detail, we suggest to go to the following website fromwhich all the daily (normal and difference) movies can be accessed:http://proba2.oma.be/ssaThis page also lists the recorded flaring events.A weekly overview movie can be found here (SWAP week 301).http://proba2.oma.be/swap/data/mpg/movies/weekly_movies/weekly_movie_2015_12_28.mp4Details about some of this week’s events, can be found further below.

Monday Dec 28

A small eruption was observed in SWAP from AR 2473 in the south west quadrant at 22:50 UTon 2015Dec28 see above SWAP image


Find a movie of the events here (SWAP movie)http://proba2.oma.be/swap/data/mpg/movies/20151228_swap_movie.mp4

Wednesday Dec 30

A small eruption was observed in SWAP observations on 2015Dec30 at 19:08 UT from AR 2473in the south west quadrant See the above SWAP imageFind a movie of the event here (SWAP movie)http://proba2.oma.be/swap/data/mpg/movies/20151230_swap_movie.mp4


Thursday Dec 31

A failed eruption was observed in SWAP on 2015Dec31 at 13:33 UT from AR 2473 from thesouth west quadrant See the above SWAP imageFind a movie of the event here (SWAP movie)http://proba2.oma.be/swap/data/mpg/movies/20151231_swap_movie.mp4

Friday Jan 01


A large eruption was seen in SWAP observations off of west limb at 23:08 UT on 2016Jan01 See the above SWAP image for contextFind a movie of the event here (SWAP movie)http://proba2.oma.be/swap/data/mpg/movies/20160101_swap_movie.mp4

3. Review of solar activity

While the only other region on disk, AR 2472, decayed during the week, solar activity was dominated bythe active region 2473 which produced several C flares and two long duration (LD) M flares. Both of theM flares were associated with coronal mass ejections and increases in the >10MeV proton fluxes.


The first long duration M1.8 flare peaked at 12:45UT December 28 and was associated with a partialhalo CME first visible in SoHO/LASCO C2 field of view at 12:12UT.


watch the movie: http://www.stce.be/newsletter/movies/CME20151228.movwatch the LASCO/C2 and difference movie: http://www.stce.be/newsletter/movies/20151230_c2_combo.mp4

It had an angular width of close to 250 degrees with primary angle to the South-West off the Sun-Earth line. Projected speeds were in the order of 600 km/s with a slightly faster component towards theSouth-East. An impact at Earth was expected in the afternoon of December 30 (around 21:00 UT) andwas recorded around midnight December 30/31. This CME initiation also caused a slight and gradualincrease of the >10MeV proton flux. It reached a peak just below 4 pfu after midnight December 28/29before subsiding.

The second long duration M2.3 flare peaked around midnight January 1/2 at 00:11UT. It was associatedwith a dimming and radio sweeps and was responsible for an increase in the >10 MeV protons and anassociated CME was detected in coronagraph data.


watch the cactus- movie: http://www.stce.be/newsletter/movies/CME20160102.movwatch the LASCO/C2 and difference movie: http://www.stce.be/newsletter/movies/20160103_c2_combo.mp4

The >10 MeV proton flux values passed the event threshold of 10 pfu around 4:30UT, peaked at 21.5pfu at 4:50UT before subsiding.

SoHO/LASCO C2 coronagraph data show a partial halo CME directed towards the South-West from23:24UT January 1 onwards. The angular extent of the core is rather limited but counting the angularextent of the shock extensions it may be interpreted as about 200 degrees (CACTUS misinterpreted andoverestimated the angular extent). Measured projected speeds are up to 1600 km/s.


4. The International Sunspot Number (28 Dec 2015 - 3 Jan 2016

The daily Estimated International Sunspot Number (EISN, red curve with shaded error) derived by asimplified method from real-time data from the worldwide SILSO network. It extends the official SunspotNumber from the full processing of the preceding month (green line). The plot shows the last 30 days(~ one solar rotation). The horizontal blue line shows the current monthly average, while the green dotsgive the number of stations included in the calculation of the EISN for each day.

5. Noticeable Solar Events (28 Dec 2015 - 3 Jan 2016)

DAY BEGIN MAX END LOC XRAY OP 10CM TYPE Cat NOAA28 1120 1245 1409 M1.8 370 CTM/1IV/1 5 247301 2310 0011 0101 M2.3 II/1 2473

LOC: approximate heliographic location TYPE: radio burst typeXRAY: X-ray flare class Cat: Catania sunspot group numberOP: optical flare class NOAA: NOAA active region number10CM: peak 10 cm radio flux


6. Review of geomagnetic activity

Solar wind conditions started the week near nominal until the arrival of the shock from the December 28CME around midnight December 30/31 at 00:02UT. As measured by ACE, total interplanetary magneticfield jumped from 6nT to 13nT while the solar wind speed jumped from 340km/s to 400 km/s. Solar windspeed kept increasing to a peak of around 500 km/s. Total magnetic field was in the 9-17nT range butwithin the sheet Bz was initially variable and remained above -10nT. With the passage of the core, lateron December 31 and January 1, the magnetic field was oriented almost directly Southward with a peakvalue of Bz of -16nT and slowly decreasing in magnitude.

In response, geomagnetic conditions reached minor storm levels locally (K Dourbes 5) and moderategeomagnetic storm levels globally (NOAA Kp 6). Solar wind conditions remained slightly elevatedthroughout the remainder of the week with quiet to unsettled geomagnetic conditions.


7. Geomagnetic Observations at Dourbes (28 Dec 2015 - 3 Jan 2016)


8. Review of ionospheric activity (28 Dec 2015 - 3 Jan 2016)

The figure shows the time evolution of the Vertical Total Electron Content (VTEC) (in red) during thelast week at three locations:a) in the northern part of Europe(N61°, 5°E)b) above Brussels(N50.5°, 4.5°E)c) in the southern part of Europe(N36°, 5°E)This figure also shows (in grey) the normal ionospheric behaviour expected based on the median VTECfrom the 15 previous days.

The VTEC is expressed in TECu (with TECu=10^16 electrons per square meter) and is directly relatedto the signal propagation delay due to the ionosphere (in figure: delay on GPS L1 frequency).The Sun's radiation ionizes the Earth's upper atmosphere, the ionosphere, located from about 60kmto 1000km above the Earth's surface.The ionization process in the ionosphere produces ions and freeelectrons. These electrons perturb the propagation of the GNSS (Global Navigation Satellite System)signals by inducing a so-called ionospheric delay.


See http://stce.be/newsletter/GNSS_final.pdf for some more explanations ; for detailed information, seehttp://gnss.be/ionosphere_tutorial.php

9. Future Events

For more details, see http://www.spaceweather.eu/en/event/future

COSPAR/ILWS workshop: science for space weather in Goa, IndiaStart : 2016-01-24 - End : 2016-01-29Understanding and being able to forecast space weather is an increasingly important aspect of ourmodern technology-reliant society. This workshop will treat all aspects of space weather, ranging fromsolar origins of transient events (CMEs, Flares, CIRs) to their propagation through the heliosphere andeffects on Earth and planetary bodies, from particle energization to forecasting particle environment andits effects on technological and biological systems, as well as solar-cycle effects and coupling of spaceweather to atmospheric response. Metrics to assess predictions will also be discussed. The workshop isstructured along the lines of the COSPAR space weather pathways and will include invited, contributedtalks and posters, as well as panel discussions and tutorials.Website:http://www.cessi.in/ssw/program.html

The Scientific Foundation of Space WeatherStart : 2016-06-27 - End : 2016-07-01Website:http://www.issibern.ch/program/workshops.html

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